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Re: Bench tests needed...



<head thumping on desk>
This has got to be the programmer's equivalent to overhauling an
engine because of a bad spark plug.
Can we say "tunnel vision"?  Because I _know_ how 8x16mult works.  I
spent a gazillion hours working on it, and thinking "Wow, this is
pretty cool", then promptly ran off and forgot about it.
Thanks...
Shannen

Ludis Langens wrote:
> 
> Shannen Durphey wrote:
> >
> > This has puzzled me for a long time:
> > LD3B5:  ldx     #0x0037
> > D3B8    ldaa    *SAC
> > D3BA    jsr     8X16mult
> > D3BD    std     *L0044
> >
> > What is this?  SAC looks like the 8 bit spark angle, but what
> > significance is 55 decimal?
> 
> "SAC" contains the angle in units of 90/256 degrees.  Just before this
> code snippet, the sixteen bit angle value in the Y register was stuffed
> into SAC.  (Actually, it also took the absolute value of the number and
> set up a flag to distinguish advance/retard.)  Locations 0x0037:0x0038
> contain the number of clock counts for 90 degrees of engine rotation.
> The 8X16mult function takes the 8 bit value in A, and the 16 bit value
> pointed to by X, multiplies them, divides the result by 256, and returns
> this in the D register.  The result is that if SAC contained say 128
> (which means 45 degrees), then D will end up with half of the value in
> 0x0037:0x0038.  This is the amount of time it takes the engine to rotate
> 45 degrees.
> 
> --
> Ludis Langens                               ludis (at) cruzers (dot) com
> Mac, Fiero, & engine controller goodies:  http://www.cruzers.com/~ludis/
> 
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